This Standard specifies Supplementary Service Call Transfer (SS-CT),
which is applicable to various basic services supported by Private
Integrated Services Networks (PISNs). Basic services are specified
in ECMA-142.

SS-CT is a supplementary service which enables a user to transform
two of that user's calls (of which one must be answered) into
a new call between the other two users of the two calls.

Supplementary service specifications are produced in three stages,
according to the method described in ETS 300 387. This Standard
contains the stage 1 and stage 2 specifications of SS-CT. The
stage 1 specification (clause 6) specifies the supplementary service
as seen by users of PISNs. The stage 2 specification (clauses
7 and 8) identifies the functional entities involved in the supplementary
service and the information flows between them.

This Standard contains two stage 2 specifications reflecting
different ways of operating the service within the network: transfer
by join and transfer by rerouteing.